Stretch method for making a tubular product

ABSTRACT

A tubular metal blank to be formed into a vehicle steering column or other corrugated tubular product is first deformed by radially inwardly moving dies to produce a plurality of substantially equally spaced shallow annular depressions separated by slightly raised crowns. The blank is then axially compressed to form and close a plurality of convolutions under a selected load within predetermined limits and to a selected closed length within predetermined limits, the variations being dependent on the strength of the material. Finally, the blank is stretched, expanding the convolutions to a plurality of generally similar spaced corrugations, with a selected stretch pressure within predetermined limits and to a selected expanded length within predetermined limits. If the end product is used as an energy-absorbing tube, the above method minimizes the variations in a selected compressive axial load required to collapse the finished column. In another embodiment, a series of annularly spaced notches are cut in the convolutions after they have been compressed to abutting configuration to determine the hoop strains developed in the walls of the finished product corrugations when subjected to the axial collapse loading.

United States Patent [72] lnventor William J. De Gain Warren, Mich. [21]Appl. No. 824,440 22 Filed May 14, 1969 [45] Patented May 4, 1971 [73]Assignee Koppy Tool Corporation Ferndale, Mich. Continuation-impart ofapplication Ser. No. 627,718, Apr. 3, 1967, now abandoned.

[54] STRETCH METHOD FOR MAKING A TUBULAR I PRODUCT 10 Claims, 11 DrawingFigs.

[52] US. Cl 29/155, 29/l63.5, 29/454, 64/1 1,72/341, 72/367, 74/492,113/116 [51] Int. Cl 823p 17/00 [50] Field of Search 29/421, 454, 163.5,155 (C); 113/1 16 (B); 72/341, 367; 138/173; 74/492; 61/1 1,29/155 (C)[56] References Cited UNITED STATES PATENTS 1,057,098 3/1913 Smith(29/454UX) 1,105,539 7/1914 Smith (29/454UX) 1,602,449 10/1926 Poe(29/163.5UX) 1,617,857 2/1927 Mallory (29/454UX) 2,032,555 3/1936 Ward29/454X 2,083,943 6/1937 Clifford... ll3/l 16(B) 2,371,991 3/1945Harding... (29/454UX) 2,800,321 7/1957 Jarret et al. 29/454X 3,326,0916/1967 Allen (29/454UX) Primary Examiner-Charlie T. MoonAtt0rney1-lauke, Gifford & Patalidis ABSTRACT: A tubular metal blank tobe formed into a vehicle steering column or other corrugated tubularproduct is first deformed by radially inwardly moving dies to produce aplurality of substantially equally spaced shallow annular depressionsseparated by slightly raised crowns. The blank is then axiallycompressed to form and close a plurality of convolutions under aselected load within predetermined limits and to a selected closedlength within predetennined limits, the variations being dependent onthe strength of the material. Finally, the blank is stretched, expandingthe convolutions to a plurality of generally similar spacedcorrugations, with a selected stretch pressure within predeterminedlimits and to a selected expanded length within predetermined limits. 1fthe end product is used as an energy-absorbing tube, the above methodminimizes the variations in a selected compressive axial load requiredto collapse the finished column.

In another embodiment, a series of annularly spaced notches are cut inthe convolutions after they have been compressed to abuttingconfiguration to determine the hoop strains developed in the walls ofthe finished product corrugations when subjected to the axial collapseloading.

' PATENIEU m 4mm 7 sum 1 or 3 FIG.2

INVENTOR. WILLIAM J. DE GAIN BY m,%w, WW

ATTORNEYS PATENTEU mm mm SHEET 2 BF 3 FIG.

FIG.5

FIG.

' INVENTOR. WILLIAM J. DE GAIN BY M, Maw/Mm ATTORNEYS CROSS REFERENCE TORELATED APPLICATIONS The present invention is a continuation-in-part ofU5. ap plication Ser. No. 627,7l8, filed Apr. 3, I967, now abandoned.

BACKGROUN D OF THE INVENTION 1. Field Of The Invention This inventionrelates to methods for making a tubular annularly corrugated member, andto a method of manufacturing an energy-absorbing tubular member having.predictable collapsing characteristics when subjected to an axialcompressive load.

2. Description of the Prior Art Tubular members having axial collapsingcharacteristics are increasingly being employed as energy absorbingstructural members in modern automotive vehicles to transmit torsionalor axial force between components attached to opposite end sections; forexample, in the steering column of an automotive vehicle.

When the impact of a collision or the like tends to throw the driveragainst the steering wheel or produce rearward displacement of vehiclestructure against the other end of the steering column, resultant forceswill tend to collapse of the column. The driver of the vehicle whenthrown against the steering wheel will experience a cushioneddeceleration as the energy of his momentum is absorbed in the workrequired to collapse the steering column. If forces against the lowerend of the column cause it to collapse, this will prevent the steeringwheel from being driven back against the driver.

There have been relatively few economical manufacturing techniquesdeveloped heretofor for producing a tubular member having sidewallswhich will collapse into a predictable pattern in reaction to apredetermined axial compressive force moving the ends of the tube wallstoward one another. It is the broad purpose of the present invention toprovide an improved method for producing a corrugated collapsible tubeof this character which is readily suitable in high-productionmanufacturing processes while at the same time producing a producthaving predictable energy-absorbing characteristics.

Further, in the manufacture of corrugated tubing generally, there havebeen no methods heretofor developed for economically and easilycontrolling the length and strength characteristics of the finishedproduct.

SUMMARY OF THE INVENTION In the preferred embodiment of the presentinvention, a selected section 'of a tubular blank for use as a vehiclesteering column or othercorrugated tubular product is first deformed bythe use of radially inwardly moving dies or the like to pro vide aplurality of substantially equally spaced shallow annular depressionsseparated by slightly raised annular crowns, this deformation being afactor which will determine both the number and the volumes ofconvolutions to be formed in the second step.

The ends of the blank are retained in press mandrels and the deformedsection is axially compremed so that the deformations fold in accordionfashion to form a plurality of annular and adjacent closed convolutions.The pressure necessary to close these convolutions, and the length ofthe section after closing, will be dependent on the material strength ofthe wall of the blank, so that the selected load and length will varywithin predetermined limits.

Next, the convoluted section is stretched to partially unfold theconvolutions, forming an annularly corrugated section, under a stretchpressure which will vary between minimum and maximum limits and to alength which will also vary between minimum and maximum limits, theactual stretch pressure and the actual finished length again beingdetermined by the strength of the material. However, proper balancing ofthe stretch pressure and length variations will produce a finishedproduct having a proper length within allowable tolerances and will besuch that a predictable axial compressive force encountered in the eventof a collision or the like will cause controlled collapse of thecorrugated section, so that it can act predictably as anenergy-absorbing device for use as a vehicle steering column or thelike. For any axial forces below that predicted, the column will besubstantially rigid and capable of performing in its intended fashionas, for example, in steering the vehicle.

In a collision or the like, if the vehicle driver is thrown against thesteering wheel with sufficient force, or if vehicle structure buckles toexert such forces against the lower end of the steering column, it willthen collapse, the kinetic energy producing the collapse being absorbedin the work of deforming the corrugations as the tube ends approach oneanother. The rate at which the opposite tube ends move toward oneanother is related to the circumferential or hoop strains developed inthe annular ridges of the corrugations.

In an optional method of forming, the blank is compressed further in thesecond step to flatten the annular walls of the adjacent convolutionsagainst each other. Then, before stretching, a series of annularlyspaced notches are cut across the outer periphery of the collapsedconvolutions. The final tubular section after stretching then has apattern of apertures in the partially unfolded corrugations which reducethe magnitude of the hoop stresses, depending on the depth and number ofnotches, thereby reducing the magnitude of the axial force required toinitiate the collapsing movement This step provides a means foradditionally closely controlling the axial strength of the tube. Thewalls of the corrugations in this type of tube will take a more angularconfiguration than in the previously described embodiment.

The preformed tubular blank may be deformed into a series of annularcorrugations successively having gradually reduced major diameters. Thiscan be done by spacing the preliminary depressions, formed in the firstdie operation, successively closer from one end to the other. Thus, thecorrugations of the finished tubular member will tend to collapse in aprogressive pattern as distinguished from a random or uncontrolledpattern which would be the case with equally spaced corrugations.

It is therefore a general object of the present invention to provide amethod for making a tubular product having a predictable collapsingcharacteristic by applying a compressive axial force to a tubular blanksufficient to move the opposite ends of the blank toward one another sothat the tube wall collapses into a predetermined convoluted pattern andthen applying a selected tensile axial force within limits to thecollapsed blank so that the convoluted section is partially unfolded toa selected axial length within limits.

' Further objects and advantages of the present invention will beapparent to one skilled in the art to which the invention pertains uponreference to the following detailed description.

DESCRIPTION OF THE DRAWINGS A more complete understanding of theinvention may be had by reference to the accompanying drawingsillustrating preferred embodiments of the invention in which likereference characters refer to like parts throughout the several viewsand in which:

FIG. 1 is a diagrammatic cross-sectional view illustrating a preferredmethod of preforming a tubular blank;

FIG. 2 is a longitudinal cross-sectional view illustrating thepreforming operation;

FIG. 3 is a longitudinal cross-sectional view illustrating the step ofapplying an axial compressive force to collapse the wall of thepreformed tubular blank into a convoluted configuration;

FIG. 4 is a longitudinal cross-sectional view illustrating the step ofstretching and partially unfolding the convolutions to the finishedcorrugated length;

FIG. 5 is a longitudinal cross-sectional view illustrating analternative step of fully collapsing the convolutions formed in. thetubular blank;

FIG. 6 is a crosssectional view taken substantially on the line 6-6 ofFIG. 5 and illustrating the-collapsed tubular blank provided with aseries of annularly spaced notches;

' FIG. 7 is a longitudinal elevational view illustrating the tubularsection of FIG. 5 after stretching;

FIG. 8'is a longitudinal cross-sectional view showing a tubular blankinitially deformed to provide progressively closer bular section.

DESCRIPTION oF TI-IE'PREFERRED EMBODIMENTS Referring first to FIGS. land 2, the preferred method of practicing the first step of inventioncomprises providing a tubular metal blank It) having sidewalls deformedso that the application of an axial compressive force on the oppositeends causes the blank 10 to collapse in a predetermined pattern.

' For purposes of illustration, the preformed blank 10 is made byradially converging a set of dies I2 thereon to simultaneously engagethe outer wall surface and deform it into a continuous series of shallowannular depressions 14 substantially equally spaced by slightly raisedannular crowns 16. Preferably the dies 12 deform the sidewalls of theblank 10 in a single stroke. The compressive force applied by the dies12 is sufiicient to deform the walls of the tube It) asshown, butinsufficient to produce a thinning or uneven metal forging of the tubewalls.

The blank lltl is preferably formed with undeformed end sections 18. Thenext step comprises applying by means of press mandrels an axialcompression to the end sections 18 so that they are forced toward oneanother as indicated by the directional arrows of FIG. 3, causing thecrowns 16 to radially enlarge as they fold about their major diameterand move axially toward one another until they abut to form theplurality of convolutions as shown, having substantially equal volumes,

the depressions 1 forming similar inner diameter convolu-- tions asshown.

Next, as shown in FIG. 4, a stretch pressure -is applied to the oppositeend sections lb of the blank 110 so that they are pulled away from oneanother, partially unfolding the con: volutions until they assume thepredetermined corrugated configuration indicated.

The stretch pressure used to expand the blank to its finished .form willbe the determining factor in predetermining that force which willproduce a controlled collapse if the column is later subjected toimpacts from a collision or the like, and the way in" which stretchpressure and length variations are balanced to minimize collapse loadvariations will be explained in relation to FIGS. It) and 11.

FIGS. 5, 6 and 7 illustrate an alternative method of practicing theinvention to additionally control the magnitude of the hoop strainsdeveloped-in each of the corrugations when the tubular'member w issubjected to an axial collapsing force. As shown in FIG. 5, theconvolutions formed from the crowns 16 are completely collapsed bycompressing of the press mandrels 20 until the adjacent convolutesurfaces are in full faceto-face abutment and disposed substantially ina plane normal to the axis of the blank 10.

While the blank I10 is so compressed, a series of preferably 3 equallyannularly spaced notches 22 are cut across the outer applied to the tube10 in the final forming step. Thus, by care- I fully selecting thenumber of notches 22 and-the'depth to which they are cut, a furthercontrol over the predetermined peripheries of each convolution by anysuitable cutting tool to a predetermined radial depth as shown in FIG.6. The notches :22 provide a series of discontinuities in theconvolutions which radially enlarge when the expanding stretch pressureis force necessary to initiate collapse of the finished column isavailable.

The blank I0 is finally axially stretched and takes the configurationshown in FIG. 7 after the notching step to produce a finished columnsimilar to that illustrated in FIG. 4, but with a carefully selectedpattern of apertures provided in the corrugations, which in the presentcase are of'a more angular nature.

FIG. 8 illustrates in exaggerated form another preferred method offorming a blank It) in which the shallow annular depressions 14 arespaced successively closer from left to right by forming progressivelyaxially shorter raised crowns 16. After the compression and theexpansion steps, the successive corrugations from left to right willconsequently have progressively smaller volumes as seen in FIG. 9 andwill vary in their resistance to collapse if later subjected to theaxial forces resulting from impacts of collision or the like. In suchevent the corrugations will collapse progressively from the relativelyweaker corrugations on the left to the relatively stronger corrugationson the right. In actual practice, the difference in spacing ofsuccessive depressions will be very slight but for clarity the drawingillustrates rather radical successively diminishing spacings, and thedepressions and intermediate crowns are of exaggerated radialdimensions.

FIG. 10 is a close variation diagram showing the compressed blank 10 ofFIG. 3 in which:

C is the center length relative to the left end of the compressed blanksection to which a mean material would compress at a selected closepressure,

I is the length to which the strongest material could be compressed atsuch selected close pressure,

P is the length to which the weakest material could be compressed atsuch selected close-pressure,

L is the maximum length to which the strongest material will actually becompressed,

I. is the minimum length to which the weakest material will actually becompressed,

V, is the differential between the P and L lengths, and

V is the difierential between the P, L2 lengths.

FIG. I1 is a stretch variation diagram showing the finally expandedblank 10 of FIG. 4 in which:

C is the length relative to the left end of the expanded blank sectionto which a means material would be expanded at a selected stretchpressure to predetennine the desired collapse load,

P is the length to which the strongest material could be expanded atsuch selected stretch pressure,

ll is the length to which the weakest material could be expanded at suchselected stretch pressure,

I. is the minimum length to which the strongest material will actuallybe expanded,

L; is the maximum length to which the weakest material will actually beexpanded,

V is the differential between the P and L lengths, and

V is the differential between the P and L lengths.

Since L, and L, are balanced about C, collapse load variations will thusbe minimized.

It will be apparent that, to establish this desired collapse load as aninherent characteristic of the finished product, the close and stretchpressures will be determined on development over a full range ofmaterial variables, with the convoluted length variations chosen tocpmpensate for the physical variations of different blank materials,thus minimizing collapse load variables. 7

Depending on the material uses, the finished length of the blank can bepredetermined within allowable tolerances, and that force which will berequired to produce a controlled collapse of the column can bepredetermined by proper selection of close and stretch pressures, withintolerable limits.

The above described system for determining pressures and lengths is aneconomical method for developing a tubular product to be used as avehicle steering column with walls having a carefully controlled axialstrength.

Although I have described only a few'embodiments of my invention, it isto be understood that various changes and modifications can be madetherein without departing from the spirit of the invention as expressedin the scope of the appended claims.

lclaim:

l. A method for making a tubular member, comprising the steps of:

a. providing a tubular blank with an intermediate section deformablesymmetrically about its axis into a predictable number of longitudinallyadjacent corrugations,

- b. applying a selected axial compression force within predeterminedlimits to said section deforming same into adjacent annularconvolutions; and to move the adjacent convolutions into close face toface contact to form substantially flat abutting wall sections,

. cutting out annularly spaced notches across the adjacent annularconvolutions at such time as the wall sections of the annular adjacentconvolutions are in abutting contact;

. subsequently applying a predetermined axial tension to said convolutedsection to partially expand said convoluted section to an approximatelyselected finished corrugated length, whereby on applying said axialtension expansion said convolutions of said wall sections will takesubstantially equal angular positions relative to the tube axis and willmeet to form angular edges having alternate lesser and greaterdiameters.

2. The method as defined in claim 1 wherein the predetermined tension isselected within minimum and maximum limits to substantially predeterminethe compressive axial load which would subsequently be required tocollapse said section when used as an energy absorbing column;

3. The method as defined in claim 1 wherein the step of providing saidtubular blank with a deformable intermediate section comprisesconverging preformed dies radially inwardly on said section to impresson said blank a plurality of axially spaced shallow annular depressionsseparated by slightly raised annular crowns thereby defining the numberand volumes of the later formed corrugations.

4. The method as defined in claim 1 wherein the step of applying axialcompression comprises applying a selected compressive force withinpredetermined limits to move the adjacent convolutions into contact toform alternate radially inwardly and outwardly facing annular loopedwall sections having respectively lesser and greater diameters.

5. The method as defined in claim 1 and in which the number and extentof said notches controls the circumferential hoop strains in saidcorrugations to predeterrnine that axial compressive force which wouldlater be required to collapse said section when used as anenergy-absorbing column.

6. A method for making a tubular. member of selected material comprisingthe steps of:

a. preforming a tubular blank to predetermine the number y and volumesof to be formed annular convolutions,

b. axially compressing said blank under a selected closing load withinpredetermined limits and to a selected closed length withinpredetermined limits, the variation depending on the strength of thematerial, to form a plurality of adjacent annular convolutions, theselected closing load being sufiicient to flatten said convolutions suchthat when said convolutions are later expanded, corrugations formed bysuch expansion will meet at annular substantially sharp angles,

c. cutting a selected number of annularly spaced notches to selecteddepths across the outer diameters of the flattened convolutions,

. subsequently axially stretching said blank. with a selected stretchpressure within irlaredeterrnined limits and to a selected expandedlengt s within predetermined limits,

the variations depending upon the strength of the material, to partiallyunfold the convolutions forming a plurality of adjacent annularcorrugations, said expanded member having apertures formed by saidlast-mentioned cutting step .in which said apertures reduce the hoopstrains of said corrugations to predetermined values when subjected to acollapse load.

7. The method as defined in claim 6 wherein the preforming stepcomprises forming a plurality of shallow annular depressions in saidblank spaced by slightly raised annular crowns.

8. The method as defined in claim 7 wherein said depressions are equallyspaced whereby the later formed convolutions will be of substantiallyequal dimensions.

9. The method as defined in claim 7 wherein said depressions areunequally spaced whereby the later formed convolutions will be ofdifferent diameters.

10. The method as defined in claim 9 wherein said depressions aresuccessively lesser spaced from one end to the other of said blank.

1. A method for making a tubular member, comprising the steps of: a.providing a tubular blank with an intermediate section deformablesymmetrically about its axis into a predictable number of longitudinallyadjacent corrugations, b. applying a selected axial compression forcewithin predetermined limits to said section deforming same into adjacentannular convolutions; and to move the adjacent convolutions into closeface to face contact to form substantially flat abutting wall sections,c. cutting out annularly spaced notches across the adjacent annularconvolutions at such time as the wall sections of the annular adjacentconvolutions are in abutting contact; d. subsequently applying apredetermined axial tension to said convoluted section to partiallyexpand said convoluted section to an approximately selected finishedcorrugated length, whereby on applying said axial tension expansion saidconvolutions of said wall sections will take substantially equal angularpositions relative to the tube axis and will meet to form angular edgeshaving alternate lesser and greater diameters.
 2. The method as definedin claim 1 wherein the predetermined tension is selected within minimumand maximum limits to substantially predetermine the compressive axialload which would subsequently be required to collapse said section whenused as an energy absorbing column.
 3. The method as defined in claim 1wherein the step of providing said tubular blank with a deformableintermediate section comprises converging preformed dies radiallyinwardly on said section to impress on said blank a plurality of axiallyspaced shallow annular depressions separated by slightly raised annularcrowns thereby Defining the number and volumes of the later formedcorrugations.
 4. The method as defined in claim 1 wherein the step ofapplying axial compression comprises applying a selected compressiveforce within predetermined limits to move the adjacent convolutions intocontact to form alternate radially inwardly and outwardly facing annularlooped wall sections having respectively lesser and greater diameters.5. The method as defined in claim 1 and in which the number and extentof said notches controls the circumferential hoop strains in saidcorrugations to predetermine that axial compressive force which wouldlater be required to collapse said section when used as anenergy-absorbing column.
 6. A method for making a tubular member ofselected material comprising the steps of: a. preforming a tubular blankto predetermine the number and volumes of to be formed annularconvolutions, b. axially compressing said blank under a selected closingload within predetermined limits and to a selected closed length withinpredetermined limits, the variation depending on the strength of thematerial, to form a plurality of adjacent annular convolutions, theselected closing load being sufficient to flatten said convolutions suchthat when said convolutions are later expanded, corrugations formed bysuch expansion will meet at annular substantially sharp angles, c.cutting a selected number of annularly spaced notches to selected depthsacross the outer diameters of the flattened convolutions, d.subsequently axially stretching said blank with a selected stretchpressure within predetermined limits and to a selected expanded lengthswithin predetermined limits, the variations depending upon the strengthof the material, to partially unfold the convolutions forming aplurality of adjacent annular corrugations, said expanded member havingapertures formed by said last-mentioned cutting step in which saidapertures reduce the hoop strains of said corrugations to predeterminedvalues when subjected to a collapse load.
 7. The method as defined inclaim 6 wherein the preforming step comprises forming a plurality ofshallow annular depressions in said blank spaced by slightly raisedannular crowns.
 8. The method as defined in claim 7 wherein saiddepressions are equally spaced whereby the later formed convolutionswill be of substantially equal dimensions.
 9. The method as defined inclaim 7 wherein said depressions are unequally spaced whereby the laterformed convolutions will be of different diameters.
 10. The method asdefined in claim 9 wherein said depressions are successively lesserspaced from one end to the other of said blank.